Oxidizing agents including sodium peroxide in phosphate flotation



OXIDIZING AGENTS INCLUDING SODIUM PER- OXIDE IN PHGSPHATE FLOTATION Ira M. Le Baron, Evanston, Ill., assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Application August 1, 1955 Serial No. 525,776

12 Claims. (Cl. 209-166) This invention relates to a process of beneficiating or concentrating the values of non-metallic minerals. More particularly, the process of the present invention relates to the beneficiating or concentrating of phosphate minerals from phosphatic ores. In general, the process of the present invention is applicable to beneficiation of any non-metallic ore such as, for example, apatite, fluorapatite, sylvinite, langbeinite, fluorspar, feldspar, and the like.

Apatite, which has a chemical composition equivalent to 3Ca (PO -CaF is the usual mineral form of phosphate found in nature. Extensive deposits of this mineral are found in Florida, Tennessee, and certain parts of the Western United States. This mineral is usually mixed in varying proportions with heavy metals, iron and aluminum compounds, and gangue materials, such as quartz, silicates, and calcium carbonate. Since all of the compounds in the mixture except for apatite can boot little, if any, nutritive value to plants and animals, a great deal of eifort has been made to develop processes for the concentration of apatite from the mined ore. Several methods involve the desliming, dewatering and separation of either pulped or unpulped material in order to effect a beneficiation and concentration of the ,phosphatic component. One commonly used method involves the reagentizing of such dewateredore with a collecting agent used in conjunction with a relatively high boiling hydrocarbon oil or liquid, together with the use of a basic com ponent such as caustic. When an aqueous suspension or pulped phosphatic rock is reagentized with a composition containing this combination and the same agitated and aerated in an aqueous suspension, the phosphatic values and components of the rock are found to rise and become segregated in the upper portion of such suspension while the siliceous values are found to settle or deposit in the lower portion of such a suspension. The beneficiated or enriched phosphatic material is withdrawn and further beneficiated and concentrated by reflotation, by the use of spirals or tables, or by other means well known to the art. The enriched phosphatic material from these beneficiation and concentrating treatments, which 'contains from 60% to 75%, and even as high as 80% of'tricalcium phosphate computed as bone phosphate of lime, is suitable as a raw material in the production of superphosphate, phosphoric acid, triple superphosphate and other phosphatic compounds.

Various methods of operating beneficiating processes of this type to improve the recovery and the grade of the phosphate in the beneficiation product have been attempted in the past. Some of the factors which control the recovery and grade of phosphate in the benefieiation product are the properties of the ore, the pH of the slurry,

nited States P t 2,826,301 Patented Mar. 11, 1958 the type and quantity of reagents and the type and quantity of aeration."

Although many non-metallic minerals are found in nature in an oxidized state, the surface of these minerals may be coated with slimes which are in a reduced state. It has been observed that when these slimes are present in the ore, considerable quantities of flotation reagents are required to beneficiate the ore unless the slimes are treated or removed in some manner. It has also been observed that in flotation and other beneficiating and concentrating operations, the pH is critical and a close control is necessary in order to obtain optimum recovery and concentration of values in the product. It is Well known that a flotation operation can also be controlled with the feed rate of the air and the degree of dispersion of the bubbles. The air is usually introduced from an outside source and diffused by an agitator impeller or some other means, so that there is an adequate number of bubbles to carry the selectively reagentized solids to the surface of the slurry. The degree of agitation should be sufficient to adequately diffuse the air to bring about contact between the bubbles and the solids to be floated, and to aid the raising of the flotation concentrate. Excessive agitation should be avoided because, even though it may improve dispersion of the air, it may also hinder the raising of the flotation concentrate. It has been shown that suflicient aeration can be generated chemically by treating a carbonate with an acid to produce CO or by electrolysis of the pulp water. By controlling the slimes, pH and air, it is possible to improve the recovery and concentration of the beneficiation product.

it is an object of the present invention to provide an improved process of beneficiating or concentrating ores.

It isa further object of this invention to provide an improved process of beneficiating or concentrating phosphatic ores.

It is a further object of this invention to provide an improved process of beneficiating or concentrating phosphatic ores by the froth flotation method.

It is a further object of this invention to treat phosphatic ore so as to improve the efiiciency of selectively reagentizing and floating the phosphatic components to the exclusion of the gangue.

A further object of this invention is to improve the beneficiation of phosphatic ores through minimizing the effects of slimes While at the same time improving the aeration of the pulp particles subjected to flotation, thus aiding in raising the flotation product to the surface.

It is still a further object of this invention to subject phosphatic ores to froth flotation while collecting a concentrate having improved sales appeal both as to grade and appearance.

Still further objects of the invention will be apparent upon a more complete understanding of the invention as hereinafter more fully described.

The reagentizing of phosphatic ores or phosphorousbearing materials for the purpose of beneficiating or con centrating these phosphatic values has been practiced for many years. The present invention is directed to the discovery of and use of an improved reagentizing composition for this purpose. After the phosphatic material, such as Florida pebble phosphate rock or any other phosphatic rock, such as Montana or Tennessee rock, has been sized to approximately 14 mesh +200 mesh and has been dewatered to approximately solids, it is subjected to the novel treatment as herein outlined. It has --b een discovered that when this iphosphatic slurry, which,

is the usual feed for negative ion flotation, is conditioned with an oxidizing agent, prior to the negative ion treatment and flotation operation, the recovery and grade of the phosphatic beneficiation product ultimately obtained can be and is improved.

Slime coatings, which are reducing in nature, frequently adhere to the surface of non-metallic minerals, for example phosphate ores. These slimes, if not treated prior to flotation, will greatly increase the quantity of flotation reagents required to obtain a satisfactory flotation prod uct. Conditioning of the feed with an oxidizing agent prior to reagentizing and flotation will convert the slimes to an oxidized state and thereby reduce the quantity of flotation reagents required to effect an eificient flotation operation.

t is preferred to treat an aqueous pulp of the flotation feed, which has a solids concentration of approximately 70%, with the required amount of oxidizing agent prior to adding the usual flotation reagents. It is possible to treat the flotation feed slurry with the oxidizing agent at the same time that the conventional flotation reagents are added, but a slightly greater quantity of flotation reagents will be required to obtain equivalent recovery and grade if this method is followed. The oxidizing agent may be added to the slurry in a solid form if desired. Generally, however, a solution of, or the liquid form of, oxidizing agent is employed.

It is well known in the art that pH control is an important factor in obtaining optimum flotation conditions. Caustic soda is usually used to adjust the pH in the negative ion flotation of phosphatic materials. If an oxidizing agent used in the practice of the instant process lowers the pH of the feed slurry below the optimum pH, the addition of caustic will raise the pH to the desired level. Similarly, if the oxidizing agent raises the pH above the optimum level, the addition of caustic solution is omitted and an acid solution, such as sulfuric acid is added to lower the I pH to the desired level. Certain oxidizing agents, such as sodium peroxide, can be used to maintain the pH at the proper level without the need for addition of any caustic or acid, or if these pH adjusting reagents are added, usually not as much is required as heretofore used.

Various oxidizing agents may be used to condition the ores prior to treatment with a negative ion flotation reagent, such as a fatty acid mixture and a frothing agent, such as fuel oil. Satisfactory results are obtained using as oxidizing agents or as mixtures of an oxidizing agent and another compound sodium peroxide, sodium peroxide and lithium fluoride, and sodium peroxide and hydrogen peroxide.

The most satisfactory results are obtained when sodium peroxide is used to condition the ore prior to treatment with flotation reagents. Sodium peroxide, not only oxidizes the slime coating and aids in attaining the desired pH of the slurry without need for additional caustic or acid, but it also serves as a source of finally dispersed gas bubbles which aid the flotation operation considerably. One of the decomposition products of sodium peroxide is oxygen. The oxygen forms as finely dispersed bubbles which attach to solid particles and carry them to the surface of the flotation slurry. Although air is supplied to the flotation machines from an outside source, it is difficult to obtain a dispersion of gas by this method that is as fine and as effective as that obtained by the decomposition of sodium peroxide in situ. Similar results are obtained when hydrogen peroxide is used to condition the ore prior to treatment with flotation reagents.

Suflicient quantity of conditioning agent must be added to the aqueous pulp of the ore to adjust the pH to the optimum level. This pH level depends upon the properties of the ore and upon the conditioning agent used. For example, in the flotation of phosphatic rock the pH of the reagentized pulp should be between about 7 and 9,

but the-preferred pH is between about 8 and about 9.

When sodium peroxide is used as the conditioning agent a satisfactory recovery and grade of the flotation product can be obtained when the reagent is added at the rate of between about 0.2 and about 2.0 pounds per ton of solids in the feed. However, the preferred rate of addition of sodium peroxide is between about 0.45 and about 0.85 pound per ton of solids in the feed.

When the conditioning agent is a mixture of sodium peroxide and lithium fluoride, a satisfactory recovery and grade of the product can be obtained when the weight ratio of sodium peroxide to lithium fluoride is about 3:2 and when the mixture is added at the rate of between about 0.2 and about 2.0 pounds per ton of solids in the feed. However, the preferred rate of addition of the sodium peroxide-lithium fluoride mixture is between about 0.45 and about 0.85 pound per ton of solids in the feed.

When the conditioning agent is a mixture of sodium peroxide and hydrogen peroxide a satisfactory recovery and grade of the product can be obtained when the weight ratio of sodium peroxide to hydrogen peroxide is about 1:6, and when the mixture is added at the rate of between about 0.5 and about 3.0 pounds per ton of solids in the feed. However, the preferred rate of addition of the sodium peroxide-hydrogen peroxide mixture is between about 1.75 and about 2.25 pounds per ton of solids in the feed.

The collecting agent used in conjunction with the above named conditioning and oxidizing agents is a negative ion or anionic active type reagent. When crude tall oil, which is a mixture of the higher fatty acids, is used as a collector, a satisfactory recovery and grade of the flotation product can be obtained when the collector is added at the rate of between about 0.3 and about 3.0 pounds per ton of solids in the feed. The preferred rate of addition of crude tall oil is between about 0.5 and about 0.75 pound per ton of solids in the feed.

The frothing agent is usually a liquid hydrocarbon, such as kerosene, diesel oil, fuel oil, the heavier solvent naphthas, crude oil, and the like. The frothing agent may be added at the rate of between about 0.1 and about 6.0 pounds per ton of solids in the feed. Under certain conditions, it is not necessary to add a frothing agent to the flotation feed. I

Phosphatic ores and other non-metallic ores previously described may be conditioned with an oxidizing agent prior to subjecting the ores to beneficiation operations other than flotation. For example, the ore may be treated with-an oxidizing. agent and other suitable reagents and then subjected to a tabling operation. If phosphatic ore is being beneficiated, a tabling operation of conventional construction will allow a collection and segregation of phosphatic material on the one hand, and siliceous and heavy mineral, bodies on the other hand. Phosphatic ore when treated with an oxidizing agent and other suitable agents may be beneficiated in a spiral operation, where the reagentized feed is conducted in a downwardly spiralling path so as to permit the phosphatic material to be selectively centrifugally moved to the outer side of the spiral pathway, while the siliceous bodies and other impurities are collected from the inner portion of the spiral pathway.

As illustrative of the character of the instant invention, but in 'nowise intending to be limited thereby, the following examples are described.

EXAMPLES I TO V The same standard conditions were used for Examples I to V except for the variations indicated in Table 1. Florida phosphate rock was beneficiated and deslimed to obtain a fraction of about -28 +200 mesh. Approximately 1000 grams (dry basis) of this fraction was diluted with water to about 70% solids, placed in a mixing chamber with the conditioning agent, and agitated for about one minute. After excess liquid was decanted, a crude tall oil collector and a fuel oil frother were added 5 to the mixing chamber. The reagentized slurry was diluted with water to about 70% solids and agitated for about one minute. The slurry was placed in a laboratory flotation cell and flotation product was collected for 45 seconds.

Table 1 Example I II III IV V Gonditloning Agent... NaqOr NarOr Nero; NerOr NaOl-I 0.2 0,5 0.8 2.0 0.5 0. 68 0. 68 0. 68 0. 68 0. 68 Frother 3.0 3.0 3.0 3.0 3.0 BPL in Feed, w ght percent.. 31. 2 32. 3 31. 2 32. 8 32. 1 Product:

Recovered, weight percent 41. 6 51. 2 51. 51. 1 20. 0 BPL, weight percent 63. 4 66. l 50. 5 50. 6 63. 5 BPL Recovery,

weight percent.-. 83. 5 88. 1 81. 5 78. 2 33. 4 Tails, BPL, weight percent 8. 86 8. 04 11. 99 15. 02 26. 80

The BPL recovery obtained in Example V using a conventional reagent may be somewhat lower than what normally would be expected under these conditions. It is believed that improper decanting of the feed after conditioning with NaOH may have caused a decrease in the BPL recovery. Nevertheless, the BPL recovery obtained when the feed has been conditioned with NaOH and properly decanted will be lower than the BPL recovery obtained by using Na O to condition the ore.

EXAMPLE VI Tennessee phosphate rock was beneficiated and deslimed to obtain a flotation feed of about +28 +200 mesh. Six hundred grams of the beneficiated rock was placed in a mixing chamber and diluted to about 70% solids. The slurry was agitated while heat was applied and while the reagents were added. The slurry was heated to about 120 F. and sodium peroxide was added. The temperature was increased to 180 F., crude tall oil was added, and about one minute later fuel oil was added. After about one minute of further agitation, kerosene and naphthenic acid were added. After about one minute the reagentized slurry was subjected to flotation in a laboratory cell and the concentrate and tails were collected. The quantity of reagents, on the basis of pounds per ton of solids, is as follows:

Table 2 Reagent:

Na 0 "lbs/ton of Solids" 0.5 Crude tall oil do 0.75 Fuel oil do 1.8 Kerosene .do 0.15 Naphthenic acid do 0.8 BPL in feed, weight percent 68.9 Product:

Recovered, weight percent 77.7 BPL, weight percent 72.5 BPL recovery, weight percent 81.9 Tails, BPL, weight percent 53.75

EXAMPLES VII TO IX The same standard conditions were used for Examples VII to IX except for the variations indicated in Table 3. About 1000 grams of Florida phosphate rock, having a size of about 28 +200 mesh, was placed in a mixing chamber, diluted to about 70% solids and then agitated. Conditioning agents were then added, and after about two minutes agitation, a crude tall oil collector was added. The reagentized slurry was agitated for about one minute and then subjected to flotation in a laboratory flotation cell. The flotation product was collected for 45 seconds.

6 Table 3 Example VII VIII IX Reagents, lbs/ton: Oonditioners- Example IX is presented for purposes of comparing the recovery and grade of products obtained when an oxidizing agent is used with the products obtained when no oxidizing agent is used.

EXAMPLE X Sodium peroxide has been used as a conditioning agent in the flotation section of a commercial scale phosphate recovery plant. Deslimed phosphate ore was conditioned with sodium peroxide, fatty acid mix and kerosene, and then beneficiated in the flotation section. Sodium peroxide was added at the rate of about 0.39 pound per ton of solids in the feed, and the fatty acid was added at the rate of about 0.92 pound per ton of solids in the feed. The pH was maintained at about 8.7. The concentrate obtained by this method analyzed 76.28% BPL (bone phosphate of lime) and 3.82% insoluble material. The product contained about 87% of the BPL from the flotatation feed. A lower BPL recovery and a product containing less BPL were obtained when sodium hydroxide Was used as a conditioning agent with the same quantity of flotation reagents.

Having now thus fully described and illustrated the invention, what is desired to be secured by Letters Patent is:

1. In the process of beneficiating an aqueous pulp of phosphate ore, the step comprising the conditioning of an aqueous suspension of the ore with an oxidizing agent containing sodium peroxide.

2. In the process of beneficiating an aqueous pulp of phosphate ore, the step comprising the conditioning of an aqueous suspension of the ore with an oxidizing agent prior to subjecting the phosphate ore to beneficiation operations, said oxidizing agent being selected from the group consisting of sodium peroxide, a mixture of sodium peroxide and hydrogen peroxide, and a mixture of sodium peroxide and lithium fluoride.

3. In the process of beneficiating an aqueous pulp of phosphate ore, the step comprising the conditioning of an aqueous suspension of the ore with an oxidizing agent and flotation reagents, said oxidizing agent being selected from the group consisting of sodium peroxide, a mixture of sodium peroxide and hydrogen peroxide, and a mixture of sodium peroxide and lithium fluoride.

4. In the process of concentrating phosphate ore by flotation operations, the step comprising the conditioning of an aqueous suspension of the ore with an oxidizing agent selected from the group consisting of sodium peroxide, a mixture of sodium peroxide and hydrogen peroxide, and a mixture of sodium peroxide and lithium fluoride prior to treating the phosphate ore with a negative ion collecting agent and a frothing agent.

5 A process as described in claim '4 wherein sufiicient oxidizing agent is added to adjust the pH of the slurry to between about 8 and about 9.

6. In the process of concentrating phosphate ore by flotation operations, the steps comprising the separation of the mined ore into a fraction of approximately 14 +200 mesh, treating an aqueous suspension of the ore with suflicient sodium peroxide to adjust the pH of the slurry to between about 8 and about 9, treating the conditioned ore with a collecting agent and a frothing agent,

and subjecting the treated ore to a froth flotation operation to recover a flotation product richer in phosphate than the feed material. e

7; In the process of concentrating phosphate ore by flotation operations, the steps comprising the separation of the mined ore into a fraction of approximately 14 +200 mesh, treating an aqueous suspension of the ore with a mixture of sodium peroxide and lithium fluoride, said mixture having a weight ratio of Na O to LiF of about 3:2, said mixture being of suflicient quantity to adjust the pH of the slurry to between about 8 and about 9, treating the conditioned ore with a collecting agent, and subjecting the treated ore to a froth flotation operation to recover a flotation product richer in phosphate than the feed material.

8. In the process of concentrating phosphate ore by flotation operations, the steps comprising the separation of the mined ore into a fraction of approximately -14 +200 mesh, treating an aqueous suspension of the ore with a mixture of sodium peroxide and hydrogen peroxide, said mixture having a weight ratio of Na O to H of about 1:6, said mixture being of suflicient quantity to adjust the pH of the slurry to between about 8 and about 9, treating the conditioned ore with a collecting agent and a frothing agent, subjecting the treated ore to a froth flotation operation to recover a flotation product richer in phosphate than the feed material.

9. In the process of concentrating phosphate ore by flotation operations, the step comprising the conditioning of an aqueous suspension of the. ore with an oxidizing agent selected from the group consisting of sodium peroxide, a mixture of sodium peroxide and hydrogen peroxide, and a mixture of sodium peroxide and lithium fluoride and at the same time adding a collecting agent and a frothing agent.

10. A process as described in claim 9 wherein suflicient oxidizing agent is added to adjust the pH of the slurry to between about 8 and about 9.

11. A process as described in claim 6 wherein the sodium peroxide, the collecting agent and the frothing agent are added simultaneously to an aqueous suspension of the ore.

12. A process as described in claim 8 wherein the mixture of sodium peroxide and hydrogen peroxide, the collecting agent and the frothing agent are added simultaneously to an aqueous suspension of the ore.

References Cited in the file of this patent UNITED STATES PATENTS 2,571,866 Greene Oct. 16, 1951 2,666,587 Runke Jan. 19, 1954 2,682,337 Hodges et al. June 29, 1954 

1. IN THE PROCESS OF BENEFICIATING AN AQUEOUS PULP OF PHOSPHATE ORE, THE STEP COMPRISING THE CONDITIONING OF AN AQUEOUS SUSPENSION OF THE ORE WITH AN OXIDIZING AGENT CONTAINING SODIUM PEROXIDE. 